In Reply.—I agree that radionuclide cisternography is often of benefit in cases of dementia being evaluated for possible shunt surgery. This technique provides information on the status of the cerebrospinal circulation that is of value in many patients suspected of having normalpressure hydrocephalus, particularly when there are atypical clinical or radiological features. Radionuclide cisternography should not be relied on, however, to make the diagnosis without regard to the other findings.1,22 Neither should it be used to exclude the diagnosis in patients who are clinically and radiologically characteristic of normal-pressure hydrocephalus. In the case under discussion, both the clinical and magnetic resonance imaging examinations supported the diagnosis of normal-pressure hydrocephalus at the time the decision to place the shunt was made. The additional information provided by radionuclide cisternography would not have been of value.Overall, data from studies of the value of radionuclide cisternography in patients suspected of having